The disclosure relates generally to carrier resins, and in particular, resins used for carrier coatings which include at least one ester functional group and at least one cyclic aliphatic group containing at least one nitrogen atom in the cyclic ring structure. Carriers having such resins in the coating exhibit high charge and excellent relative humidity (RH) sensitivity of charge to changing environmental conditions. The nitrogen containing groups have been shown by modeling to have a much lower barrier to charge transfer than the best performing conventional resins, especially with silica as a toner additive on the toner, and thus will provide for the desired higher toner charge.
Toners can comprise at least a binder resin, a colorant and one or more external surface additives. The external surface additives can be added in small amounts. Examples of external surface additives include, for example, silica, titanium dioxide, zinc stearate and the like.
The properties of a toner are influenced by the materials and amounts of the materials of the toner. The charging characteristics of a toner also can depend on the carrier used in a developer composition, such as, the carrier coating.
Toners having triboelectric charge within the range of about −30 μC/g to about −45 μC/g may be achieved by including smaller-sized silica particles as external additives, for example silica particles having average sizes of less than about 20 nm, such as, for example, R805 (˜12 nm) and/or R972 (˜16 nm) (Evonik, NJ). However, developability at areas of low toner area coverage degrades over time. That has been attributed to the smaller-sized additives being impacted into the toner surface over time.
The problem with smaller-sized additives may be addressed by using larger-sized additives, i.e., additives having a size of about 40 nm or larger such as, for example, RX50 silica, RX515H silica or SMT5103 titania (Evonik, NJ). However, such toners do not exhibit as high a triboelectric charge and also exhibit charge through. New carrier coatings are being developed that enable higher charge developers, particularly those with larger-sized additive packages. However, when such developers are tested at low area coverage followed by high area coverage, the developers tend to exhibit low or wrong sign toner due to charge through, i.e., the incumbent toner in the device becomes less negative or even of the wrong sign, that is, the opposite charge, i.e., positive, and the new (fresh) toner added may charge very negative. The presence of low charge and/or wrong sign toner can result in objectionable background.
There remain problems with providing high charge with good relative humidity (RH) sensitivity of charge to changing environmental conditions for carrier coating resin designs. For example, there remains a need to tune the charge of the carrier resin to produce higher charge. Further, many toners contain silica as a surface additive. Silica can be a substantial charge driver for a toner, although silica is known to be RH sensitive. Hence, it is a goal to provide new carrier designs that work well with silica to improve RH sensitivity, while maintaining high charge.
In addition, a high carbon content and high carbon:oxygen (C/O) ratios provide the best RH sensitivity, but charge is insufficient without the addition of heteroatoms such as nitrogen. However, because nitrogen is polar, such linear alkyl substituted nitrogen compounds tend to make RH sensitivity worse while tending to soften the resin and lower Tg. Thus, there is also a need for higher carbon content nitrogen-containing compounds that do not compromise the hardness and do not lower Tg.